Preparation of lower tetraalkyl quaternary ammonium nitrate



United States atent lice 3,079,433 PREPARATEGN 9F LOWER TETRAALKYL This invention relates to a process for the preparation of a quaternary ammonium nitrate and more particularly to the preparation of a lower tetraalkyl quaternary amr'n'on'ium nitrate.

Lower tetraalkyl quaternary ammonium nitrates have aroused considerable interest in the field of rocket propulsion. These compounds are used primarily as components of liquid rocket fuels, particularly in liquid monopropellants Where they Contribute to both the oxidizing component and fuel component. The most common method for the preparation of these compounds consists of reacting a tetraalkyl quaternary ammonium halide with silver nitrate in an aqueous solution. in this process the silver nitrate reacts with the tetraalkyl quaternary ammoniurn forming tetraalkyl quaternary ammonium nitrate and an insoluble silver halide which precipitates out and is separated by filtration. Since such a process consumes both silver and the halide, it is costly and thus economically impractical for a large scale operation.

it is, therefore, an object of this invention to provide an efiicient process for the preparation of a lower tetraalkyl quaternary ammonium nitrate. A further object is to provide a process which does not require expensive reactants and is adaptable to a large scale operation.

The above and other objects are attained according to the invention by intermiring an aqueous solution of a lower tetraalkyl quaternary ammonium halide with an es sentially water insoluble amine nitrate salt, such as a primary amine nitrate and a substituted pyridonium nitrate. Upon intermiXin-g the aqueous solution of the tetraalkyl quaternary ammonium halide with the water insoluble amine nitrate, the tetraalkyl ammonium halide is converted to the nitrate salt, while the amine nitrate salt is converted to a chloride salt. The tetraalkyl quaternary ammonium nitrate formed is soluble and remains in the aqueous solution. The reacted amine salt which is insoluble is separated from the aqueous solution. The product is then recovered from the aqueous solution. The reacted amine salt may be converted to the nitrate salt and reused.

The term amine, as used hereafter, refers to the primary amine salts and the substituted pyridonium salts. The term quaternary ammonium, as used hereafter, refers to the tetraalkyl quaternary ammonium salts. The term immiscible, as used herein in reference to the organic solvent and water, means that the organic solvent and water are essentially insoluble in each other.

While the amine nitrate salts may be dispersed within the aqueous solution of the quaternary ammonium halide to efiect the reaction, it is generally preferred todissolve the amine nitrate salt in a diluent, such as an organic sovent, which is immiscible with the water and in which the quaternary ammonium salt is insoluble. In using the two solutions, the quaternary ammonium nitrate product formed by being contacted with the amine salt in the hydrocarbon diluent is soluble in aqueous solution and thus remains in the aqueous solution. The amine nitrate being converted to the chloride salt is essentially insoluble in the water and will remain in the hydrocarbon phase. Thus, methods and equipment similar to the known techniques used in liquid-liquid extraction may be used to intermiX the solutions and carry out the reaction. A batch orcontinuous process may be used. It is generally [are 2 ferred'to use a continuous countercu'rrent multistage operation.

The reacted amine salt remaining in the hydrocarbon phase may be regenerated to the nitrate form by treating the hydrocarbon phase with a solution of nitric acid. When the hydrocarbon phase is treated with an aqueous solution of nitric acid, two phases are also formed. The amine salt remains in the hydrocarbon phase, while the unreacted acid and other reaction products remain inthe aqueous phase. The so-treated hydrocarbon phase, after separation from the aqueouspha'se, can be'again returned to be contacted with more of the quaternary ammonium halide reactant.

When a dispersion of the amine salt is used instead of a solution, the reacted amine is substantially insoluble in water and may thus be recovered by mechanical separation, such as filtration. The recovered reacted amine s'alt which will be inchloride form may also be regenerated by treatment with nitric acid and reused in the process.

Lower tetraalkyl quaternary ammonium nitrates having a total of from 4 to 7 carbon atoms and a general formula:

LR: R4 where'R R R and R represent an alkyl radical having from 1 to 4 carbon atoms may be thus prepared. Illustrative examples of these compounds, which are finding wide utility as liquid rocket fuels, are tetrarnthyl ammonium nitrate, trimethylisopropyl ammonium nitrate, and die-thylclirnethyl ammonium nitrate.

In the preparation of the'quaternary ammonium nitrate, a corresponding quaternary ammonium halide is used as a reactant. The halide has a total of from 4 to 7 carbon atoms and a general formula:

\N X'- Rs Ri' where R R R and R represent an alkyl radical of from 1 to 4 carbon atoms and X represents a halogen selected from the group consisting of bromide and chlorine. A bromide salt is preferred. These halide reactants may be prepared by known suitable methods, such as by the reaction of a tertiary amine with a monoalkyl halide. While the concentration of the quaternary ammonium halide solution used may be as high as saturation, a solution containing from l0 to 20 weight percent of the quaternary ammonium halide is preferred. With solutions containing the preferred concentration of the halide salt, substantially complete conversion of the quaternary ammonium halide may be obtained very readily. At concentrations containing greater than 20 weight percent, the solution may have to be contacted in more than one stage to obtain substantially complete conversion. Since the quaternary ammonium nitrate remains in the aqueous phase and must be recovered from the solution, it is desirable to obtain a-solution containing the highest concentration: possible of the salt. Thus while solutions having as little as 0.01 weight percent of the ammonium quaternary halide may be used, the disadvantage or" trying to'recover the resulting product from such a' low concentration makes it desirable to use a. solution containing at least 5 weight percent and preferably at least lO per-cent of the quaternary ammonium halide salt.

The amine salts used should be preferably essentially insoluble in water. While the solubility of the amine -salt rnay not materially afiiect the reaction, its presence in the aqueous solution requires the employment of additional steps in the recovery of the quaternary ammonium nitrate product from the solution. 'A'lso generally the amine salt which dissolves in the solution is not recovered so that it represents a loss. The size of the aliphatic moieties on the amine and pyridonium compounds determines to a great extent the solubility of the compound. Generally, primary amines with less than 12 carbon atoms in the alkyl group will have a relatively high solubility and thus are seldom used. Also pyridoniurn compounds having alkyl radicals which total less phatic primary amines containing from to carbon atoms and pyridonium compounds containing aliphatic radicals having a total of 20 to 25 carbon atoms are preferred.

In a preferred method of carrying out the invention, the primary amine or pyridonium compound is dissolved in a suitable inert solvent immiscible with water, such as aliphatic hydrocarbon solvents as naphtha, kerosene, mineral spirits and the like. A solution of the amine salts containing from about 1 mole to 3 moles of the amine salt per liter of solution may be employed. A 2 molar solution of the amine or pyridonium compound in an aliphatic hydrocarbon solvent, such as kerosene, is preferred.

The primary amines are generally available as free amine salts and the pyridonium compounds as bromide salts. These amine salts may be also used, but they first must be converted to the nitrate form. After dissolving the amine salts in the solvent, the solution is contacted with nitric acid to convert the amine salt to the nitrate form. Rec cle solutions of amine salts which are in the halide form are likewise converted to the nitrate by using a nitric acid solution. Preferably a stoichiometric amount of around 4 molar nitric acid solution is used. In contacting the amine solutions with the nitric acid, conventional liquid-liquid extraction equipment, such as mixersettlers and the like, may be used. The treated amine solution containing the amine in the nitrate form remains in the hydrocarbon solvent. It is separated from the nitric acid and then intermixed with the aqueous solution of the quaternary ammonium halide.

Conventional liquid-liquid-extraction equipment may likewise be employed in contacting the amine nitrate solution with the aforementioned aqueous solution of the quaternary ammonium halide. To insure complete conversion of the quaternary ammonium halide to the nitrate ithout the use of a large excess of the amine solution, a counter-current multistage contact operation having from 2 to '4 contact stages is generally employed.

After the aqueous quaternary ammonium halide solution is contacted with the amine nitrate solution, an aqueous phase obtained containing the quaternary ammonium nitrate 'is separated from the hydrocarbon phase. The quaternary ammonium nitrate product is recovered by known methods from the aqueous phase. The desired product may be recovered from the aqueous phase, for example, by extraction or more conveniently by evaporation and crystallization.

In contacting the quaternary ammonium halide with the amine nitrate salt, generally room temperatures are used. A temperature above 60 C. is seldom used since the extraction of the product from the hydrocarbon phase becomes less efficient at the higher temperatures. While temperatures below room temperature are operative, sufficient advantage is not. gained to offset the additional cost to operate at the lower temperatures.

The following examples further illustrate the invention but are not to be construed as limiting it thereto.

Example I Docosyl amine was dissolved in kerosene to give a 2 molar solution of the amine. With about milliliters of this amine solution, 100 milliliters of a 4 molar nitric acid solution were intermixed to convert the amine to the nitrate salt. The treated kerosene solution was separated from the nitric aqueous solution by decantantion.

The so-treated kerosene solution containing the amine in the nitrate form was then contacted with milliliters of an aqueous solution of trirnethylisoprop'yl ammonium bromide in Water having a 0.9% molar concentration (17 Weight percent) of the quaternary ammonium salt. The amine solution and the aqueous trimethylisopropyl ammonium bromide solution were agitated for about 15 minutes and then allowed to settle. The hydrocarbon phase and aqueous phases obtained upon settling were separated. Hie aqueous phase was analyzed and found to contain a 0.83 molar concentration (14.1 weight percent) of trimethylisopropyl ammonium nitrate. By employing successive contact stages substantially complete conversion of the trimethylisopropyl ammonium bromide may be obtained.

Example II In a manner similar to that in Example I, 100 milliliters of a 2 molar solution of N-tetradecyl-4-(5-nonyl) pyridonium bromide in kerosene was contacted with nitric acid to convert the pyridonium compound to the nitrate salt. The so-treated pyridonium solution in kerosene was then contacted with 100 milliliters of a 0.966 molar (16 weight percent) aqueous solution of trimethylisopropyl ammonium bromide. The hydrocarbon phase and aqueous phase obtained upon intermixing of the two solutions were separated. The aqueous phase obtained was analyzed and found to contain a 0.66 molar concentration (11.2 Weight percent) of trimethylisopropyl ammonium nitrate.

In a manner described above, tetramethyl ammonium bromide or chloride and diethyldimethyl ammonium bromide or chloride may be used in place of the trimethylisopropyl ammonium bromide to prepare the corresponding tetramethyl ammonium nitrate and diethyldimethyl ammonium nitrate, respectively. Also inplace of the docosyl amine and N-tetradecyl-4-(5-nonyl) pyridonium bromide nitrate other amines containing aliphatic alkyl radicals of from 12 to 50 carbon atoms may be employed.

What is claimed is:

l. A process for the preparation of a lower tetraalkyl quaternary ammonium nitrate, which comprises intermixing an aqueous solution of a tetraalkyl quaternary ammonium halide having the total of from 4 to 7 carbon atoms and having the general formula:

R3 R4 where R R R and R represent a lower alkyl radical having from 1 to 4 carbon atoms and X represents a halogen selected from the group consisting of chlorine and bromine with an amine nitrate salt selected from the group consisting of primary aliphatic amine nitrates and alkyl substituted pyridonium nitrates to convert the tetraalkyl quaternary ammonium halide to a corresponding tetraalkyl quaternary ammonium nitrate, and recovering the tetraalkyl quaternary ammonium nitrate from the mixture.

2. A process for the preparation of a lower tetraalkyl quaternary ammonium nitrate, which comprises intermixing an aqueous solution of a tetraalkyl quaternary ammonium halide having the total of from 4 to 7 carbon atoms and having the general formula:

R3 R4 where R R R and R represent a lower alkyl radical having from 1 to 4 carbon atoms and X represents a i halogen selected from the group consisting of chlorine and bromine with a solution of an essentially water insoluble amine nitrate salt selected from the group consisting of primary aliphatic amine nitrates and alkyl substituted pyridonium nitrates in an organic solvent immiscible with water to form a heterogeneous mixture containing an aqueous phase and a non-aqueous phase and to convert the tetraalkyl quaternary ammonium halide in the aqueous solution to the corresponding tetraalkyl quaternary ammonium nitrate, separating the aqueous phase from the non-aqueous phase, and recovering the tetraalkyl quaternary ammonium nitrate from the aqueous phase.

3. A process according to claim 2 wherein the solution of the essentially water insoluble amine nitrate is of an amine nitrate containing alkyl radicals having a total of from 12 to 50 carbon atoms dissolved in an aliphatic hydrocarbon solvent.

4. A process according to claim 3 wherein the aqueous solution contains from 10 to 20 weight percent of the tetraalkyl quaternary ammonium halide and the aliphatic hydrocarbon solution is a 1 to 3 molar solution of the essentially water insoluble amine nitrate.

5. A process according to claim 4 wherein the tetraalkyl quaternary ammonium halide is trimethylisopropyl ammonium bromide.

6. A process according to claim 5 wherein the amine nitrate is docosyl amine nitrate.

7. A process according to claim 5 wherein the amine nitrate is N-tetradecyl-4-(S-nonyDpyridonium nitrate.

8. A process for the preparation of a lower tetraalkyl quaternary ammonium nitrate, which comprises intermixing an aqueous solution of a tettaalkyl quaternary ammonium halide having the total of from 4 to 7 carbon atoms and having the general formula:

Ra Rt where R R R and R represent a lower alkyl radical having from 1 to 4 carbon atoms and X represents a halogen selected from the group consisting of chlorine and bromine with a solution of an essentially water insoluble amine nitrate selected from the group consisting of primary aliphatic amine nitrates and alkyl substituted pyridonium nitrates in an aliphatic hydrocarbon solvent to form a heterogeneous mixture containing an aqueous phase and a hydrocarbon phase and to convert the tetraalkyl quaternary ammonium halide in the aqueous phase to form a heterogeneous mixture containing an aqueous nitrate, separating the aqueous phase from the hydrocarbon phase, recovering the tetraalkyl quaternary ammonium nitrate from the aqueous phase, treating the hydrocarbon phase with an aqueous nitric acid solution to convert the amine salt in the hydrocarbon phase to an amine nitrate, and recycling the so treated hydrocarbon phase to be intermixed with more aqueous tetraalkyl quaternary ammonium halide solution.

9. A process according to claim 8 wherein the aqueous tetraalkyl quaternary halide solution is a trimethylisopropyl ammonium bromide solution containing from 10 to 20 weight percent of the bromide and the aliphatic hydrocarbon solution of an essentially water insoluble amine nitrate is a 1 to 3 molar solution of docosyl amine nitrate in kerosene.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,079,438 February 26, 196

Ray S. Long It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 59, and column 5, line 4, for "aliphatic", each occurrence, read alkyl column 5, line 5, after "an" insert inert column 6, line 12, for "aliphatic" read alkyl lines 17 and 18, for "to form a heterogeneous mixture containing an aqueous nitrate" read to the corresponc ing tetraalkyl quaternary ammonium nitrate same column 6, line 29, for "aliphatic" read alkyl Signed and sealed this 14th day of April 1964.

(SEAL) Attest:

ERNEST w SW .EDWARD J, BRENNER Attesting Officer Commissioner of Patents 

1. A PROCESS FOR THE PREPARATION OF A LOWER TETRAALKYL QUATERNARY AMMONIUM NITRATE, WHICH COMPRISES INTERMIXING AN AQUEOUS SOLUTION OF A TETRAALKYL QUATERNARY AMMONIUM HALIDE HAVING THR TOTAL OF FROM 4 TO 7 CARBON ATOMS AND HAVING THE GENERAL FORMULA: (R1-N(-R2)(-R3)-R4)(+) X(-) WHERE R1, R2, R3, AND R4 REPRESENT A LOWER ALKYL RADICAL HAVING FROM 1 TO 4 CARBON ATOMS AND X REPRESENTS A HALOGEN SELECTED FROM THE GROUP CONSISTING OF CHLORINE AND BROMINE WITH AN AMINE NITRATE SALT SELECTED FROM HE GROUP CONSISTING OF PRIMARY ALIPHATIC AMINE NITRATES AND ALKYL SUBSTITUTED PYRIDONIUM NITRATES TO CONVERT THE TETRAALKYL QUATERNARY AMMONIUM HALIDE TO A CORRESPONDING TETRAALKYL QUATERNARY AMMONIUM NITRATE, AND RECOVERING THE TETRAALKYL QUATERNARY AMMONIUM NITRATE FROM THE MIXTURE. 